burr & the direction of grinding

[Robert]

Hi everyone,
I am new in this forum, so forgive me if I ask stupid questions.
I tried to find answers for my questions, but maybe not looking in the right place.

After almost 50 years of sharpening knives I still struggle with the concept of the *burr*:
(i) Assume one sharpens from the spine to the edge of a knife: the wheel causes an abrasion of the steel; as the abrasion 'rips out' tiny particles of metal, some of the steel will get smeared in direction to the edge (like butter on bread) and forms a tiny lump - the burr.
(ii) if the knife is turned to the other side (still spine-to-edge), the same occurs. Why is there not another burr from the other side? There is only one burr - is it the agglutination of two burrs? As there is no thermic forming because of the low speed and the water cooling, how can this happen?
(iii) Assume grinding from the edge to the spine of a knife:
assuming the butter-on-bread assumption in (i) is correct, there shouldn't appear a burr on the edge but instead maybe something more in direction of the spine. BUT there IS a burr at the edge!
(iv) This seems to imply that the butter-on-bread-smearing analogy is wrong for edge-to-spine grinding (at least). But where does the burr then come from? Is it metal that is pressed by the turning wheel 'over' the apex of the edge such that it agglutinates on the other side?
(v) If this would be true, we would have two different types of burr - at least from their origination (and possibly to be corrected by differing procedures) ...

[John Hancock Sr]

Not sure about the butter on bread analogy but yes, the steel will deform as the grit passes over the edge and form a burr as the steel edge "turns up" opposite the edge exposed to the grit. The burr always occurs on the side opposite to the edge exposed to the grit. In theory grinding away from the edge will result in a larger burr since the grit is forcing the metal away from the edge. The finer the grit (and the sharper the grit) the less of a burr since the deformation of the metal is less. Honing is said to be the "removal of the burr" but it is more than that I think. I generally hone the opposite side to the burr first since I think that it polishes away the burr rather than "rips it off" that way I think you will probably get a finer edge. If you watch the Tormek Innovation videos on you tube you will get a lot more information on the formation of the burr and its removal.

[Robert]

Thanks, John,

"... the steel will deform as the grit passes over the edge and form a burr as the steel edge "turns up" opposite the edge exposed to the grit ..."

Okay, forming of the burr (spine-to-edge grinding):
the steel is pushed by the grinding wheel, thus gets somehow a little bit more liquid (temporarily) and 'flows' from the inner edge to the apex; like the butter which is more liquid/deformable than he bread is smeared to the fringe of the bread.
Once the liquidized steel has reached and passed the apex, it forms an initial burr.
As more steel is deformed and pushed over the apex it agglutinates with the already existing burr and makes it bigger.
The burr is very thinly connected to the edge (at least as thin as the apex); therefore the pushing from the wheel bends it to the other side of the the edge.

Is this how the burr comes to existence in spine-to-edge grinding?

[cbwx34]

Not sure if it'll help, but have you seen the Science of Sharp website?  It has a section on burr formation (and removal) that may help.

[Ken S]

Welcome to the forum, Robert. I am no expert on burrs, however, I would offer one suggestion. In my opinion, a bench chisel is the the ideal tool for studying sharpening with a Tormek. A chisel with a single straight bevel about 19 mm (3/4") width is the simplist tool to sharpen. For these two exercises do not worry about exact bevel angles, square grinding, secondary (micro) bevels or having a perfectly flat and polished back. Concentrate on the bevel. The bevel of a chisel is large enough that you can easily see and feel the ffects of grinding. Feel free to stop and start, observing the stages of burr formation. You can also observe things like scratch pattern changes when you grade your grinding wheel and use the leather honing wheel. You can use the support bar as a rest to sharpen with the wheel moving trailing the edge.

I whole heartedly endorse studying the online classes. For many years, we had the knowledge in the handbook. The evolving knowledge seemed to primarily remain at the factory. I do not believe this was intentional; I just think until Covid there was no push to use video. I have watched most of the online classes numerous times. I always learn more each time. They are an excellent learning resource. They are structured to involve the listeners. Ask your questions; I do.

In the basic honing class, Sebastien announced the intention of eventually doing an advanced honing class. I look forward to this.

Keep interested and keep us posted.

Ken

[Robert]

Hi, many thanks.
I just had a look at science of sharp.
Absolutely mind blowing pictures; however the author is very cautious about drawing generic conclusions.
I like his careful approach, but personally I am more interested in a descriptive model of burrs:
how they emerge, can be detected & classified and, lastly, can be removed.

[cbwx34]

Hi, many thanks.
I just had a look at science of sharp.
Absolutely mind blowing pictures; however the author is very cautious about drawing generic conclusions.
I like his careful approach, but personally I am more interested in a descriptive model of burrs:
how they emerge, can be detected & classified and, lastly, can be removed.

You pretty much just described the Knife Deburring Book... may want to look at that.

[John_B]

When you look further into burr formation you will also find the burr is also dependant on the steel. Soft inferior blades are almost impossible to deburr effectively as the bur just moves rather than being honed. Super steels at the other end of the spectrum require a special technique as shown in the previously mentioned book by Vadim

[tgbto]

The abrasive also plays a fundamental role in "rooting out the burr" as Vadim used to put it. I find that the Tormek PA-77 paste is very effective, whereas other seem to have that tendency to draw out a wire burr forever...

[Robert]

... I would offer one suggestion. In my opinion, a bench chisel is the the ideal tool for studying sharpening with a Tormek....

Hello, Ken
Thanks for the idea, but as I'm a strange guy, I'm interested in understanding the problem first and then finding a practical solution.
I've been sharpening woodworking tools and knives for almost 50 years and I can do it reasonably well.
But what still puzzles me, or frustrates me, is that I don't know really what I'm doing - or more precisely: why I'm doing it this way and not another way (well, its  stems from a mix of trial-and-error, good advice ... and not so good advice).
I am interested in a theory of the formation of ridges, their typology and then their practical removal.
Many thanks, Robert

[Robert]

You pretty much just described the Knife Deburring Book... may want to look at that.

Thanks for that. I bought it.
This is the best thing I have read so far. To my taste, the author jumps a bit too much from topic to topic (and back again), but if you write it down in an orderly fashion, it would be exactly what I'm looking for at the moment.
Best, Robert.